Can you sniff out your mate? Previous research suggests a women’s mate preference is based on odor. Sounds odd, right? But our sense of smell is regulated by something called major histocompatibility complex (MHC), which are genes that are key to our immune system and our autoimmunity. When it comes to organ donation, it’s important to closely match MHC profiles between organ donors and recipients to reduce the risk of transplant rejections. But for a future breeding partner, having MHC profiles that are different maximizes the genetic diversity of future offspring. So where are we going with all this? A new study suggests that birth control pills, which originally liberated women from unwanted pregnancies, may sabotage this very primal ability to “smell” the best mate.

Blood was drawn from 193 women split into a placebo and pill group and 97 men for MHC genotyping.  Between days 10 and 14 days of their menstrual cycle, the women smelled six jars containing the odor from three MHC-similar and three MHC-dissimilar men. Odor pleasantness and intensity was rated on a seven-point scale and they were asked if the smell made them want the man as a long term partner at two different times, three months apart. Women on the pill were more likely to want a man with an MHC-similar odor as a long-term mate compared to the control group. Many women on the pill are likely trying to avoid having children until they find Mr. Right, but what if the pill actually impairs the ability to find him?

One weakness in the study was the scores given by women on the pill were higher than those in the control groups, which may confound the results. But if this study is indeed true, it raises some other important questions. While the pill may no longer be responsible for weight gain, is it responsible for the divorce rate? Do other drugs affect a woman’s mate selection? And if the pill confuses our ability to sniff out “the one,” our tongues may have to take on the important job of tasting genetic diversity while kissing our potential future mate.